Method for insulating a magnet wire with an aromatic titanate modified nylon

ABSTRACT

A magnet wire enamel having improved runnability and insulating properties is described comprising nylon containing a titanate selected from the group consisting of (RO) 4  Ti, dimers, trimers, and mixtures thereof where R is an aromatic group. The nylon can be a sole coat, outermost coating, or bond coat.

This is a division of copending application Ser. No. 758,913 filed on July 25, 1985 U.S. Pat. No. 4,588,784.

DESCRIPTION TECHNICAL FIELD

The field of art to which this invention pertains is polyamide coating compositions, and particularly nylon coating compositions on insulated magnet wire substrates.

BACKGROUND ART

Because of their relative low cost and the desirable handling properties they provide to polymer insulated magnet wire, nylon topcoats have been used in the magnet wire area for several years. However, such coatings are not without problems. For example, on high temperature wire such as magnet wire coated with polyester base coats, nylon overcoats have suffered from such things as ring cracks (circular cracks perpendicular to the major axis of the coated wire) particularly in dry weather and such cracks can cause catastrophic wire failure. Furthermore, because of the relatively low solidification point of nylon, temperature changes can cause great difficulty in providing a smooth coating on wire. Part of this problem results from the fact that when applying plural coatings of the nylon, successive coats redissolve previously applied coats, thus producing smoothness problems.

Accordingly, what is needed in this art is a nylon composition which overcomes such problems.

DISCLOSURE OF INVENTION

The present invention is directed to an improved magnet wire enamel composition comprising nylon modified by reaction with aromatic titanate dimers, trimers, and mixtures thereof. The aromatic titanate reacts with the amine and carboxyl groups on the nylon molecule resulting in a nylon modified dimer with both improved application to magnet wire substrates and improved wire properties after application to the magnet wire substrates. The aromatic titanates are typically reacted into the nylon in an amount of about 0.25% to about 10% by weight of the nylon present in the enamel composition.

Another aspect of the invention is electrically insulated magnet wire containing a plurality of polymer layers of insulation where at least one of the layers comprises the above-described nylon enamel.

Another aspect of the invention comprises a method of forming polymer insulated magnet wire having a plurality of polymeric insulating layers where at least one of the layers is the nylon material described above.

These and other advantages of the present invention will become more apparent from the following description.

BEST MODE FOR CARRYING OUT THE INVENTION

Any nylon material can be catalyzed with the titanate described herein. Typically nylon 6; nylon 11; nylon 6,6; nylon 6,12; etc. are used.

The aromatic titanates used have the formula (RO)₄ Ti, where R is an aromatic group, and including polymeric titanates (typically dimers and trimers) thereof. As made (and purchased commercially) the aromatic titanates typically contain minor amounts of their dimer, trimer, etc. Similarly, the polymeric titanates, when made (and purchased commercially) typically contain minor amounts of the monomer, and other polymeric forms (e.g. dimer contains trimer etc.). Preferred titanates are cresylic, phenolic, and derivatives such as triakyl (e.g. ethyl, propyl etc.) phenolic, xylenolic, halogenated (e.g. chlorinated, brominated, etc.) phenolic, etc. The dimers and trimers would typically be linear (or branched) and chain extended through the --TiO-- groups, e.g., ##STR1## Mixtures of the above materials may also be used. Typically the nylon layer is used as an overcoat on such things as standard polyester (such as THEIC polyester), polyurethane or polyvinyl formal resins.

Although not wishing to be bound by any particular theory it is believed that the aromatic titanate-nylon reaction occurs as follows: ##STR2## where ##STR3## represents the nylon moiety.

This new molecule ##STR4## is very stable because bonding two carboxyl ##STR5## groups to a titanium center uses up all the coordination sites on the titanium. ##STR6##

This molecule, which we will refer to as a nylon dimer, has a chemistry of its own when applied to the wire substrate. For example, when applied to a previously applied base coat such as an hydroxyl rich polyester as discussed above, the following reactions take place: ##STR7## The base coat surface is hydroxyl rich and can react with one or two of the remaining aryloxy groups on the titanium nylon dimer. The above equation is written for the reaction of two aryloxy groups.

In a sole nylon coat or in the body of the film which does not interact with other layers the following reaction takes place: ##STR8## where the O on the Ti reacts with available ##STR9##

While the polymers according to the present invention can be used on any electrical conductor they are preferably used on wires and specifically on magnet wires. The wires are generally copper or aluminum and range anywhere from 4 AWG to 42 AWG (American Wire Gauge) in diameter, with 18 AWG being the most commonly coated wire. Wire coatings can be anywhere from 0.1 to 5 mils or any thickness desired and preferably about 3.2 mils on 18 AWG wire. As stated above the coatings can be used as part of a multicoat system in combination with conventional polymer insulation such as polyesters, polyurethanes, polyvinyl formal, polyimides, polyamideimides, etc. and combinations thereof. The polymer coatings can also contain lubricants either externally on the nylon or admixed with the nylon.

Typical multicoat systems include such things as THEIC polyester base coats with nylon topcoats with the nylon comprising about 2% to about 25% of the total thickness. When used as a bond coat, i.e. an intermediate layer between two additionl layers of polymer insulation (such as a polyurethane base coat, the nylon bond coat, and a polyvinyl butyral topcoat, i.e. a solderable composition) the nylon typically represents about 5% to about 10% of the total wire product.

The enamels according to the present invention can be applied by any conventional means such as coating dies, roller or felt application with viscosity adjustments made accordingly. Viscosity adjustments can be made by dilution with appropriate enamel solvents or diluents. Such solvents are typically cresylic acids, and N-methyl pyrrolidone, N,N-dimethyl or N,N-diethyl formamide and N,N-diethyl acetamide, along with any conventional hydrocarbon diluents such as xylene, Solvesso™ 100 (Exxon) or D59™ hydrocarbon (Drake Petroleum Company).

Conventional ovens can be used to heat treat the magnet wire after application of the nylon. Typical inlet oven temperatures are of the order of 500° F. to 700° F., preferably about 580° F. and outlet oven temperatures of about 800° F. to 1100° F., and preferably about 900° F. are used for drying and curing.

In order to demonstrate the improved and unexpected properties of nylon modified with the aromatic titanate according to the present invention, experiments were run to ascertain the effects of various additives on the enamel.

The following examples show the properties of wire made from the aromatic titanate modified reprocessed nylon (e.g. scrap nylon 6,6 fibers repelletized).

These enamels were tested on 18 AWG copper with THEIC polyester base coat in a Df (250°) range varying from 0.03 to 0.17.

EXAMPLE 1

One and four tenths (1.4) part per hundred by weight of tetracresyl titanate (TCT) was reacted with reprocessed nylon made from repelletized scrap nylon 6,6 fibers. A 15% by weight mixture of this modified nylon was made up with cresol, phenol, and/or xylene by mixing for one-half hour to form a homogeneous solution. This mixture was coated on 18 AWG wire as described above. The change in properties were as shown in the table below:

    ______________________________________                                                                Mandrel                                                              Df (250°)                                                                         Pull Dry                                                ______________________________________                                         Enamel                     Failed at                                           Without TCT                all conditions.                                     Same Enamel    0.08        14                                                  With 1.4% TCT  0.20        12                                                  ______________________________________                                    

In this table Df values of between about 0.12 and about 0.28 represent a cured enamel with values less than about 0.11 representing overcure. In the mandrel pull column, values greater than 10 represent a "pass".

EXAMPLE 2

A similar enamel was tested with 1.4% polymeric TCT (primarily dimer and trimer). The results are as shown below:

    ______________________________________                                                                  Mandrel                                                             Df (250°)                                                                          Pull Dry                                              ______________________________________                                         Enamel With     0.07          8                                                No TCT          0.12         Pass                                                              0.20         Pass                                              Enamel With     0.08         14                                                1.4% TCT        0.20         12                                                ______________________________________                                    

In a concurrent set of experiments TCT was added to monoethanolamine equilibrated nylon enamel which contains a relatively large amount of acetic acid. When this is done the following reaction occurs which strongly competes with dimer formation.

    CH.sub.3 COOH+Ti(OR).sub.4 →(CH.sub.3 COOH).sub.2 Ti(OR).sub.2

In order to determine what changes had been made to the nylon itself, modified and unmodified nylon enamels were run as sole coats. Essentially there was no change in general properties of the nylon coating when TCT was added as a modifier.

The Tg and melt point of modified and unmodified nylons were compared and found not to have been changed by the dimerization. This absence of change was to be expected. TCT treated nylon still passes the HCl acid blush test.

As stated above besides providing improved sole coats and topcoats for various polymer constructions, the modified nylon according to the present invention also produces an improved intermediate layer (bond coat) in multiple layer constructions.

Although this invention has been shown and described with respect to detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention. 

I claim:
 1. A method of coating a magnet wire substrate comprising applying to an electrically conductive wire substrate at least one layer of an enamel composition comprising nylon reacted with 0.25% to 10% by weight based on the weight of the nylon present in the enamel composition of a titanate selected from the group consisting of (RO)₄ Ti, dimers, trimers and mixtures thereof where R is an aromatic group.
 2. The method of claim 1 wherein said aromatic group is selected from the group consisting of cresol, phenol, xylenol, and alkylated and halogenated derivatives thereof.
 3. The method of claim 1 further comprising applying a layer of polyester to said electrically conductive wire substrate prior to application of said nylon.
 4. The method of claim 1 further comprising applying a layer of polyurethane on said electrically conductive wire substrate prior to applying said nylon layer and applying a layer of polyvinyl butyral over said nylon layer. 